1. Field of the Invention
The present invention relates to an optical head to be used in an information recording medium such as an optical disc device.
2. Description of the Related Art
In the general optical disc device, there is used an optical head comprising a semiconductor laser, an optical system, and a photo-detector. A laser beam emitted from the semiconductor laser is led to the optical disc through the optical system, and reflecting light reflected on the optical disc is led to the photo-detector through the optical system again, thereby reproducing data recorded in the optical disc.
The photo-detector comprises a photo-detector element for converting reflecting light into an optical signal, and a fixing block for fixing the photo-detector element. The fixing block is secured to an optical base of the optical disc device. The photo-detector is arranged such that the in-plane direction of the fixing block is perpendicular to the direction of the optical axis of light incident upon the photo-detector element.
In such a photo-detector, the fixing block is shifted in a state that the fixing block is not completely fixed, thereby adjusting two axis in-plane direction perpendicular to the direction of the optical axis. Then, a focusing lens for converging reflecting light on the photo-detector element is moved in the direction of the optical axis. Thereby, the focal position in the direction of the optical axis is adjusted to be set to a suitable position.
Since the adjustment of the conventional photo-detector is based on the signal of the photo-detector element, it is impossible to individually adjust the positions of the two axis in-plane directions and the focal position. Due to this, there is needed work for positioning the focusing lens and the fixing block correctly while the position of the focusing lens and that of the fixing block are adjusted at the same time. After positioning, the focusing lens is fixed to the optical base by a holding spring or a pressing screw. Thereafter, the focusing lens is adhered to the optical base.
However, the focusing lens slightly moves in the direction perpendicular to the optical axis when the focusing lens is fixed by a pressure bar spring or a pressure screw. Due to this, there is a problem that the focal position on the photo-detector shifts. Since the spot position on the photo-detector element must be extremely correctly adjusted, adjusting work is further needed even if the focal position slightly shifts. Due to this, it becomes difficult to perform adjusting work.